Which histologic type of breast cancer is often difficult to detect on mammography due to a diffuse growth pattern?

• A. Ductal carcinoma in situ
• B. Infiltrating lobular
• C. Fibroadenoma
• D. Medullary carcinoma

Answer: (B)

Breast cancers that grow diffusely through the stroma without forming a discrete mass are often missed on mammography. Infiltrating lobular carcinoma is classic for this pattern: tumor cells invade in a single-file, discohesive fashion through the breast tissue with minimal desmoplastic reaction, so they don’t create a well-defined lump or clear architectural distortion. This diffuse infiltration can make mammographic detection challenging, and the disease may present as subtle thickening or architectural distortion, sometimes even bilaterally.

Ductal carcinoma in situ, by contrast, often shows suspicious calcifications on imaging and stays noninvasive within the ducts, making it more detectable. Fibroadenoma is benign and typically appears as a well-circumscribed, easily identified mass. Medullary carcinoma can form a mass as well, sometimes with distinct margins, though its imaging features are variable.